Jiri Palecek wrote:
> Kimon Hoffmann wrote:
>
>> What I'd like to know is whether there is some way to make HalfWorking
>> work with fully qualified calls to func() like the one in
>> cool_algorithm_2(), besides the obvious solution to move HalfWorking
>> together with the function overload into the default_impl namespace.
>
> Fully qualified no, but something similar is possible. It is quite
commonly
> used:
>
> using default_impl::func;
> func(x);
>
> This will call ::func(const HalfWorking&) for arguments of type
HalfWorking,
> and default_impl::func for anything convertible to DefaultType.
Yes, I am aware of that, but until I stumbled across the problem above I
wasn't fully aware of the implications.
> The usual use for this idiom is std::swap, because you want to use
std::swap
> for anything that doesn't have a swap function, and find the overloads
by
> ADL where there is one. Also, you should use it for all std functions
that
> operate on standard types if you want to overload them for your types
and
> find the overloads by ADL (you obviously cannot move your overloads to
> std::) For example, you can create class your_ns::matrix, which would be
> eg. a real matrix. Then, you can define a function
Thanks, this is a keeper :). And now that I learned the lesson the hard
way, I don't believe I'll ever miss this in the future ;).
> Note that you also need this if a C library leaves its definitions in
the ::
> scope. For example, abs(0.5) might call ::abs(int) which is really sad
:-(
Since the code is intended for a library, the main reasons for why I
wanted to make it work with fully qualified names were:
1. I did not want to force a particular usage pattern on the user (i.e.
not force him to use the idiom you described above).
2. I wanted to avoid matching to unexpected global overloads like
::abs(int). Although for user defined types such mismatching is highly
unlikely to happen in practice.
Best regards,
Kimon
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